The present invention relates generally to the construction of components employed in medium and high voltage electrical distribution systems and pertains, more specifically, to an improvement in the structure and arrangement of the coupling components of a bushing well in such an electrical distribution system.
Connections in underground power distribution systems, such as between cables and transformers, are generally accomplished with specially designed separable male and female electrical connectors, such as loadbreak connectors and deadbreak connectors. Such cable connectors, used in conjunction with 15, 25 and 35 kV systems, generally include a power cable elbow connector and a bushing insert. The elbow connector has one end adapted for receiving a power cable and another end adapted for receiving an insertion end of the bushing insert. The opposite end of the bushing insert, which extends outward from the elbow connector, may in turn be received in a bushing well of a transformer, for example.
Currently, most bushing wells are constructed with an integral threaded stud which is unitary with the electrical contact element of the bushing well. At one end, the stud serves as a threaded connector for mechanically coupling and electrically connecting a bushing insert to the bushing well. At its opposite end, the stud is provided with another threaded connection for further connecting the well to another electrical component, such as a transformer. Bushing wells are typically mounted within such other electrical components by applying a wrench, such as a spanner wrench, around an external shoulder portion of the well and rotating the well so that the stud threadably engages the electrical component.
One drawback with these prior art bushing wells is the damage sometimes caused by the tool applied to the outer surface of the well during installation. In particular, application of a spanner wrench often causes chipping or cracking of the metalized epoxy material on the shoulder portion and other surfaces of the well that are critical to sealing.
Another drawback is that during assembly of the bushing insert with the bushing well, the threaded connection between the components sometimes is over tightened, resulting in the stud breaking from the electrical contact element. In addition, in disassembling a bushing insert from a bushing well, the threaded connection sometimes is found to be seized and the result, once again, is a severing of the threaded stud from the electrical contact element of the bushing well. In other instances, the thread of the stud has become damaged, as by galling, thus rendering the stud useless in attaining the desired coupling and connection. In each of these instances the end result is a requirement for replacement of the entire bushing well, leading to considerable down-time in the electrical distribution system and considerable extra expense.
Other drawbacks with bushing wells of the prior art relate to the problems encountered during manufacturing. Typically, these connectors are made by transfer molding of an epoxy material. Epoxy molding is expensive and it is often difficult to attain a good bond with other essential rubber and metal components. Moreover, as mentioned above, metalized epoxy surfaces are prone to chipping and cracking during installation and are easily damaged if the bushing well is dropped or bumped against other hard surfaces. Furthermore, as compared to rubber, metalized epoxy is not as desirable in a wet environment.
Accordingly, it would be desirable to provide a bushing well that can be installed on or mounted within another electrical component with minimal risk of damaging or marring critical surfaces of the well. It would also be advantageous to provide a bushing well stud which enables simplified removal and replacement of a damaged or broken stud without requiring replacement of the entire bushing well. It would be further desirable to provide a bushing well with reduced manufacturing costs and that will be less prone to damage when handling.